In recent times, cryotherapy has gained increasing importance in the treatment of rheumatic diseases. Hereby, a preferably dry flow of gas at a temperature as low as -180.degree. C. is applied to the joints or body parts to be treated. According to the functional principle of the equipment used, this gas flow consists of cold air, cold nitrogen gas, or a mixture of the two. In order to guide this cold gas flow to the patient and direct it to the body parts to be treated, a hose is required, which must fulfill a number of specific requirements.
First, the hose must thermally be so well insulated that no significant cooling of the exterior surface of the hose results from the gas throughflow which may be as cold as -180.degree. C. The insulation must be so efficient that practically no water condensation occurs under continuous operation, even at high ambient humidity. Good insulation simultaneously guarantees effective utilization of the refrigerant. In spite of such good insulation, the hose must also have sufficient flexibility at operational temperature, so that the therapist can uniformly and comfortably reach the body regions to be treated without moving the patient. In spite of this high flexibility, however, the hose must also have sufficient mechanical stability. Nor must the weight of the hose be too great, since comfortable handling would be negatively affected by too great weight. Further, it is desirable that the cold capacity of the hose is low, in order to minimize the cooling time and the refrigerant losses. Further, it is also desirable that the hose is inexpensive, i.e. that it can easily be assembled from standard materials. Naturally, these requirements also apply to the hose-end pieces.
The currently used hoses do not fulfill all of these requirements. For instance, an insulation proven in cryotechnology may be glued onto the lines. However, it hardens at low temperatures, so that it is not usable for flexible hoses. If, on the other hand, the hoses are insulated by means of loose bulk insulation material, there is the disadvantage that over time, this material will accumulate in the low-lying areas. Here, the insulation material will be compacted, which causes changes in the insulation properties. The highest incidence of such compacting will naturally occur on hoses that are frequently moved, as is the case in cryotherapy. Superinsulated hoses are too expensive, and their bending radius is too great. Corrugated and smooth tubes of synthetic material also have too great bending radii, disregarding the fact that they will also have to be provided with additional insulation. Corrugated metal tubes have too great cold capacity and are heavy. In addition, they require much space for insulation.